Since the first report and due to its handiness and wide scope, the Suzuki-Miyaura (SM) cross coupling reaction has become a routine methodology in many laboratories worldwide. With respect to other common transition metal catalyzed cross couplings, the SM reaction has been so far less exploited as a tool to introduce an acyl function into a specific substrate. In this review, the various approaches found in the literature will be considered, starting from the direct SM acylative coupling to the recent developments of cross coupling between boronates and acyl chlorides or anhydrides. Special attention will be dedicated to the use of masked acyl boronates, alkoxy styryl and alkoxy dienyl boronates as coupling partners. A final section will be then focused on the acyl SM reaction as key synthetic step in the framework of natural products synthesis.
A new class of strigolactone analogues has been synthesized. They differ from known molecules, both of natural and synthetic origin, in two main features. The conjugated system extends from the enol ether bridge to the A ring, the B ring is a heterocycle while the C ring is a cyclic ketone instead of a g-lactone. The key step of the synthesis is a Nazarov cyclization on activated substrates. Bioassays using Orobanche seeds have revealed that all the molecules strongly stimulate germination; in particular the oxygen containing analogues are the most active. Interestingly, some of the new molecules show fluorescent properties.
The upregulation of low-density lipoprotein (LDL) transporters in tumour cells has been exploited to deliver a sufficient amount of gadolinium/boron/ligand (Gd/B/L) probes for neutron capture therapy, a binary chemio-radiotherapy for cancer treatment. The Gd/B/L probe consists of a carborane unit (ten B atoms) bearing an aliphatic chain on one side (to bind LDL particles), and a Gd(III)/1,4,7,10-tetraazacyclododecane monoamide complex on the other (for detection by magnetic resonance imaging (MRI)). Up to 190 Gd/B/L probes were loaded per LDL particle. The uptake from tumour cells was initially assessed on cell cultures of human hepatoma (HepG2), murine melanoma (B16), and human glioblastoma (U87). The MRI assessment of the amount of Gd/B/L taken up by tumour cells was validated by inductively coupled plasma-mass-spectrometric measurements of the Gd and B content. Measurements were undertaken in vivo on mice bearing tumours in which B16 tumour cells were inoculated at the base of the neck. From the acquisition of magnetic resonance images, it was established that after 4-6 hours from the administration of the Gd/B/L-LDL particles (0.1 and 1 mmol kg(-1) of Gd and (10)B, respectively) the amount of boron taken up in the tumour region is above the threshold required for successful NCT treatment. After neutron irradiation, tumour growth was followed for 20 days by MRI. The group of treated mice showed markedly lower tumour growth with respect to the control group.
The gold(I)-catalyzed cyclization of N-Boc-protected 6-alkynyl-3,4-dihydro-2H-pyridines, prepared by the Sonogashira coupling of lactam-derived enol triflates or phosphates, provides vinylogous amides, which are useful intermediates in the synthesis of natural compounds. The Au(I)-catalyzed reaction is carried out with Ph3PAuOTf as a catalyst and proceeds via a 6-endo-dig cyclization to form a vinylgold species that after protodeauration generates a cyclic carbamate intermediate. This intermediate is in most cases not isolated, but the addition of a base to the reaction mixture rapidly and quantitatively delivers the target vinylogous amide. The first synthesis of a natural compound from Sonneratia hainanensis has been accomplished by this approach.
Abstract.In this study the synthesis and characterization of a new dual, imaging and therapeutic, agent is proposed with the aim of improving the efficacy of Boron Neutron Capture Therapy (BNCT) in cancer treatment. The agent (Gd-B-AC01) consists of a carborane unit (ten boron atoms) bearing a cholesterol unit on one side (to pursue the incorporation into the liposome bi-layer), and a Gd(III)/1,4,7,10-tetraazacyclododecane monoamide complex on the other side (as MRI reporter to attain the quantification of B/Gd concentration). In order to endow the BNCT agent with specific delivery properties, the liposome embedded with the MRI/BNCT dual probes has been functionalized with a peghilated phospholipid containing a folic acid residue at the end of the PEG
Synthesis and characterization of 14 new 2,2′-bipyridine metal complexes
fac
-M(bpy-R)(CO)
3
X (where M = Mn, X = Br or M = Re, X = Cl and R = -CF
3
, -CN, -Ph, -PhOH, -NMe
2
) are reported. The complexes have been characterized by NMR, IR spectroscopy and elemental analysis. Single crystal X-Ray diffraction structures have been solved for Re(dpbpy)(CO)
3
Cl (dpbpy = 4,6-diphenyl-2,2′-bipyridine) and Re(hpbpy)(CO)
3
Cl (hpbpy = 4-(2-hydroxy-phenyl)-6-phenyl-2,2′-bipyridine). Electrochemical behaviors of the complexes in acetonitrile under Ar and their catalytic performances for CO
2
reduction with added water and MeOH have been investigated by cyclic voltammetry and controlled potential electrolysis. The role of the substituents on the electrochemical properties and the related over potentials required for CO
2
transformation have been analyzed. The complexes carrying only electron withdrawing groups like -CF
3
, -CN totally lose their catalytic activities toward CO
2
reduction, whereas the symmetric -NMe
2
substituted and push-pull systems (containing both -NMe
2
and -CF
3
) still display electrocatalytic current enhancement under CO
2
atmosphere. The complexes carrying a phenyl or a phenol group in position 4 show catalytic behaviors similar to those of simple M-bpy systems. The only detected reduction product by GC analysis is CO: for example,
fac
-Re (bpy-4,4′-NMe
2
)(CO)
3
Cl gives CO with high faradic efficiency and a TON of 18 and 31, in absence of external proton source and with 5% MeOH, respectively. DFT calculations were carried out to highlight the electronic properties of the complexes; results are in agreement with experimental electrochemical data.
In this study, the Huisgen reaction has been used to functionalise a carborane cage with a lipophilic moiety and a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) ligand to obtain a new Gd boron neutron-capture therapy (BNCT)/magnetic resonance imaging (MRI) agent. The introduction of the triazole units has been accomplished under both heterogeneous conditions, by the use of a Cu-supported ionic-liquid catalyst, and homogeneous conditions. The ability of the Gd complex of the synthesised ligand to form stable adducts with low-density lipoproteins (LDLs) has been evaluated and then MRI has been performed on tumour melanoma cells incubated in the presence of a Gd-complex/LDL imaging probe. It has been concluded that the high amount of intracellular boron necessary to perform BNCT can be reached even in the presence of a relatively low-boron-containing LDL concentration.
C-(2-Benzyloxy)-ethyl-C'-N-tert-butoxycarbonyl-aminomethyl-o-carborane (8), a potentially useful intermediate for BNCT, has been synthesised. This intermediate can be readily functionalised with several biological vectors and MRI contrast agents. In this work intermediate 8 has been functionalised with a palmityl chain for lipophilic targeting and with Gd(III)-DOTAMA-C(6)-NH(2) as MRI detector. This combination yielded Gd(III)-C-palmitamidomethyl-C'-DOTAMA-C(6)-o-carborane (14) as a dual MRI-BNCT agent.
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